Muffler for internal combustion motor vehicles

ABSTRACT

A muffler has a housing provided with irregularly arranged ridges computed by an FEM computer program. The ridges are regularly bounded, simple geometric figures, such as circles, circular rings, circular ring segments, rectangles or trapezoids. The size and position of the ridges are selected in such a way that the lowest resonance frequency of the muffler housing is greater than or equal to the dominant excitation frequency of the internal combustion engine over its entire rpm range.

BACKGROUND OF THE INVENTION

The invention concerns mufflers for motor vehicles with internal combustion engines, which comprise at least a muffler housing, an intake pipe, an exhaust pipe, and possibly internal walls and/or pipes. The muffler housing is provided with irregularly arranged ridges computed by an FEM computer program.

In designing the geometry of a muffler for motor vehicles, whether it is an intake muffler or a rear muffler, the acoustic requirements must be coordinated with the spatial situation in the engine compartment or under the chassis. The spatial situation in particular results in muffler housings with an oval to cubically flat cross section. To prevent the free vibration of large-area sheet metal parts of the muffler housing and the unimpeded radiation of sound, especially low-frequency sound, from these parts, the sheet metal parts of the muffler housing are provided with impressions. Compare, for example, DE 197 46 553 A, EP 0 324 891 A, BE 653 635 A, JP 49129034 A, JP 07259531 A, or U.S. Pat. No. 2,835,336. The impressions in the muffler housing sheet metal that are described in these documents were determined essentially empirically. Although this made it possible to achieve a certain amount of reduction in the sound radiation from the surface of the muffler housing, the results were not optimal.

The German journal “ATZ und MTZ”, Special Edition October 2003, pp. 39-40, describes a topography optimization for the rear muffler of an exhaust system for internal combustion engines, which was performed with the use of the computer program “Optistruct”, which is sold by the US company Altair Engineering. This computer program, which is based on the finite-element method (FEM), is able to automatically optimize a sheet metal surface in such a way that the lowest resonance frequency becomes as high as possible. The higher the resonance frequency is, the lower the subjectively and objectively perceived noise is.

Starting from the predetermined shape and size of the muffler housing, the computer program “Optistruct” computes the impressions in the housing surface that result in the highest possible resonance frequency. The impressions in the housing surface that have been computed in this way can be designated as irregularly bounded, irregularly positioned, and irregularly elevated ridges.

Due to its similarity to the spots on the hide of a cow, this ridge pattern is also known as “cow-spot design.” The term “Kassel ridge” is also used.

Although the acoustic results of the ridge patterns determined with these kinds of computer optimization programs are outstanding, the deep-drawing dies needed to create them are also complicated and expensive, since simple machining methods cannot be used to produce the irregularly bounded and irregularly elevated male and female dies. This is unsatisfactory.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a muffler of the aforementioned type, whose sound radiation from the surface of the muffler housing is minimized, but which can be produced with much simpler and less expensive tools.

This goal is achieved by a muffler having a muffler housing, an intake pipe attached to the housing, an exhaust pipe attached to the housing, and selectively internal walls and/or pipes. The muffler housing has irregularly arranged ridges computed by an FEM computer program. The ridges are regularly bounded, simple geometric figures. The muffler housing has a lowest resonance frequency at least equal to a dominant excitation frequency of the internal combustion engine over the engine's entire RPM range.

The present invention is based on the predetermined task of minimizing the sound radiation from the surface of the housing by means of a computer optimization program, such that, however, the ridge pattern is limited to simple geometric shapes that can be produced essentially by the standardized metal machining methods of turning and milling.

These simple geometric shapes are preferably circles and circular rings, segments of circles and circular rings, and polygons, especially rectangles. These shapes are dimensioned and positioned by the computer optimization program in such a way that the lowest resonance frequency over the entire rpm range of the internal combustion engine is above its dominant excitation frequency by the greatest possible amount, so that the sound radiation of the surface of the housing is minimized.

Comparisons between mufflers in accordance with the invention and mufflers with the so-called cow spot design have shown, surprisingly, that the acoustic differences are barely measurable. However, the production costs are quite different.

In accordance with an advantageous refinement of the invention, the ridges can also penetrate each other.

Surprisingly, it was found that the ridges can also be formed as letters or characters of any desired character set, e.g., Latin, Arabic, Japanese, etc., characters, Egyptian hieroglyphs, etc. Numerals and special symbols have also been found to be suitable. However, these characters cannot be confused with serial numbers, manufacturer's marks, etc., that are customarily applied, since these are not irregularly arranged.

It is also possible to position the ridges in series.

According to another embodiment of the invention, the muffler housing is produced from only one layer of sheet metal. Conventional mufflers use double layers of sheet metal to reduce the radiation of solid-borne sound by means of the friction between the pieces of sheet metal.

Surprisingly, it was also found that the wall thickness of the sheet metal can be significantly reduced, namely, down to 0.7 mm, without an unacceptable rise in the radiation of solid-borne sound. In this regard, it doesn't matter whether the muffler housing consists of two shells or is wound from one piece of sheet metal.

Other features and advantages of the present invention will become apparent from the following description of the invention refers to the accompanying drawings.

The invention is explained in greater detail below with reference to the embodiments illustrated in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first muffler that has been optimized for minimal sound radiation;

FIG. 2 shows measured values of a before-after comparison for an optimized muffler;

FIG. 3 shows a second muffler that has been optimized for minimal sound radiation; and

FIG. 4 shows a third muffler that has been optimized for minimal sound radiation.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a first exhaust muffler for an internal combustion motor vehicle. The housing 1 has an externally flat, cubic cross section. The exhaust gases enter the housing 1 through an intake pipe 2 and leave it through an exhaust pipe 3. Partitions and internal pipes of types which in themselves are already well known are provided inside the housing 1. Their position and stiffness affect the resonance frequencies of the housing 1.

An optimized ridge pattern is impressed in the surface of the muffler housing to reduce the high level of sound radiation from the surface of the housing caused by the large and only slightly curved sheet metal surfaces. This ridge pattern consists of regularly bounded, simple geometric figures. The drawing shows circular rings 4, segments of circular rings 5, rectangles 6 and trapezoids 7. The two rectangular ridges 6 partially penetrate each other to form a T-shaped structure.

FIG. 2 shows the result of the acoustic optimization measures in a before-after comparison. The optimized curve (broken line) is as much as 10 dB below the initial curve (solid line).

FIG. 3 shows another muffler that has been optimized for minimal sound radiation by virtue of a shift of the resonance frequencies to higher values. Exclusively circles 8 of equal size are present as ridges. This makes it possible for the deep-drawing and stamping tools to be especially simple. The parallel rectangular ridges 9 serve the purpose of holding partitions in the interior of the housing 1.

FIG. 4 shows a third example of a muffler that has been optimized for minimal sound radiation. The ridge pattern consists of “letters” and “numerals” of a character set, which have been irregularly positioned by an FEM program in such a way that the lowest resonance frequency is above the dominant excitation frequency of the internal combustion engine.

Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims. 

1. A muffler for an internal combustion motor vehicle, comprising: a muffler housing; an intake pipe attached to the housing; and an exhaust pipe attached to the housing, the muffler housing having irregularly arranged ridges computed by an FEM computer program, the ridges being regularly bounded, simple geometric figures, the muffler housing further having a lowest resonance frequency at least equal to a dominant excitation frequency of the internal combustion engine over the engine's entire rpm range.
 2. The muffler in accordance with claim 1, and further comprising at least one of the group consisting of internal walls and internal pipes.
 3. The muffler in accordance with claim 1, wherein the ridges are uniformly elevated.
 4. The muffler in accordance with claim 1, wherein the geometric figures of ridges are formed as at least one of the group consisting of circles, circular segments, circular rings, and circular ring segments.
 5. The muffler in accordance with claim 1, wherein the ridges are formed as polygons.
 6. The muffler in accordance with claim 5, wherein the ridges are formed as rectangles.
 7. The muffler in accordance with claim 1, wherein the ridges are formed as characters of any desired character sets.
 8. The muffler in accordance with claim 1, wherein at least two of the ridges penetrate one another.
 9. The muffler in accordance with claim 1, wherein at least two of the ridges are arranged in series.
 10. The muffler in accordance with claim 1, wherein the ridges are at least partially elevated.
 11. The muffler in accordance with claim 1, wherein the muffler housing has a single layer wall.
 12. The muffler in accordance with claim 1, wherein the muffler housing has a wall with a thickness of less than 1 mm.
 13. The muffler in accordance with claim 1, wherein the muffler housing has a wall consisting of two shells.
 14. The muffler in accordance with claim 1, wherein the muffler housing has a wall wound from one piece of sheet metal.
 15. The muffler in accordance with claim 1, wherein parallel rectangular ridges are provided as mounts for a partition. 